1. Field of the Invention
This invention pertains generally to cab signal apparatus and, more particularly, to railroad vehicle cab signal apparatus. The invention also pertains to processors including redundant field programmable gate arrays.
2. Background Information
In railroad transportation systems, it is often desirable to transmit information to a railroad vehicle by the use of cab signaling. The information desired to be transmitted is encoded into a track signal current, which is transmitted to the railroad vehicle through the rails. When the track signal current reaches the vehicle, the signal information may be detected and the information utilized on-board the vehicle.
Some of the cab signal information transmitted may be of a nature that is desirable to be known by those on-board the railroad vehicle and/or may be information which is redundant with wayside signaling information. However, in some instances, it may be desirable that the cab signal information transmits track signal aspects, such as speed commands, to the vehicle, which are vital to the operation of the vehicle, along with track conditions that affect the operation of the vehicle. For example, four track signal aspects may be transmitted by the cab signal and each track signal aspect may have an associated maximum speed at which a train may travel into the next block. For example, the four track signal aspects may be “clear”, “approach-medium”, “approach” and “restricting”.
This information can be received by the railroad vehicle through an antenna usually positioned in front of the lead axle, which is inductively coupled to the cab signal current that is in the rail in front of the lead axle. The lead axle tends to act as a shunt between the rails and, therefore, the positioning of the cab signal antenna or inductive coupling is usually done in close proximity to, but in front of the lead axle. Other cab signal pick-up systems may also be utilized.
Some cab signal carrier frequencies of the rail current can be at frequencies of 60 Hz and 100 Hz, although a wide range of other suitable frequencies may be employed. Changes from existing cab signal carrier frequencies on projects require the hardware design of a new filter printed circuit board (PCB) for each new carrier. This can be a laborious process, which includes designing, prototyping, testing, verifying and releasing a new filter PCB for each new project that requires a new carrier frequency.
In addition to a filter, a conventional cab signal apparatus also includes a demodulator connected to the filter for receiving an output signal and retrieving a code signal from a cab signal component thereof. The code signal includes cab signal aspects for assisting with the operation of the railroad vehicle. Also, a decoder is connected to the demodulator to generate a track aspect signal corresponding to the code signal received from the demodulator.
All new projects that have new aspect definitions (e.g., carrier modulation rates) require application software changes to a decoder PCB. Furthermore, such software requires testing, verification and validation before being released to program and install one or more programmable memory components on the decoder PCB.
Historically, the use of programmable logic devices (e.g., Complex Programmable Logic Devices (CPLD) and Field Programmable Gate Arrays (FPGAs)) has not been present in safety-critical designs due to low confidence in the performance of the devices as a result of the lack of a method to formally verify that the devices are working as designed and implemented. Hence, FPGAs are believed to be relatively new to safety critical systems.
U.S. Pat. No. 5,984,504 discloses in its Background Information that instrumentation and control systems utilize diverse redundant primary and backup control mechanisms, in which the processors and/or the software utilized therein are different, in order to preclude common mode failures. In the case of control mechanisms incorporating digital processors, different types of processors (e.g., from different manufacturers) are used to run different routines (e.g., implemented in different software languages) implementing common algorithms.
U.S. Pat. No. 5,984,504 also discloses a protection subsystem employing diverse processors to protect a critical process, such as a nuclear reactor pressure vessel. The critical process has one or more characteristics, such as conditions of the pressure vessel and a plurality of parameters, such as temperature and level, each of which is representative of a characteristic. A first processor and a corresponding first parameter are substantially different from a second processor and a corresponding second parameter. The diverse processors employ different respective parameters and substantially different mechanisms to provide similar respective protection outputs, which are redundant relative to the characteristic. In this manner, a variety of common mode failures between the redundant processors are obviated. Voting mechanisms combine the processor outputs to effect a safety or protection function, such as integrated protection logic for a nuclear reactor trip.
Although diverse redundant control mechanisms are known, further improvements are possible.
There is room for improvement in railroad vehicle cab signal apparatus.
There is also room for improvement in processors including field programmable gate arrays.